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Aortic stenosis (AS) is narrowing of the aortic valve obstructing blood flow from the left ventricle to the ascending aorta during systole. Causes include a congenital bicuspid valve, idiopathic degenerative sclerosis with calcification, and rheumatic fever. Untreated AS progresses to become symptomatic with one or more of the classic triad of syncope, angina, and exertional dyspnea; heart failure and arrhythmias may develop. A carotid pulse with small amplitude and delayed upstroke and a crescendo-decrescendo ejection murmur are characteristic. Diagnosis is by physical examination and echocardiography. Asymptomatic AS in adults usually requires no treatment. Once symptoms develop, surgical or percutaneous valve replacement is required. For severe or symptomatic AS in children, balloon valvotomy is effective.
Etiology
Aortic sclerosis, a degenerative aortic valve disease with thickening of aortic valve structures by fibrosis and calcification initially without causing significant obstruction, is the most common cause of AS in elderly patients. Over years, aortic sclerosis progresses to stenosis in as many as 15% of patients. Aortic sclerosis resembles atherosclerosis, with deposition of lipoproteins, inflammation and calcification of the valves; risk factors are similar (see Arteriosclerosis: Risk Factors).
The most common cause of AS in patients < 70 yr is a congenital bicuspid aortic valve. Congenital AS occurs in 3 to 5/1000 live births and affects more males; it is associated with coarctation and rapid dilatation of the ascending aorta causing dissection.
In developing countries, rheumatic fever is the most common cause in all age groups. Supravalvular AS caused by a discrete, congenital membrane or hypoplastic constriction just above the sinuses of Valsalva is uncommon. A sporadic form of supravalvular AS is associated with a characteristic facies (high and broad forehead, hypertelorism, strabismus, upturned nose, long philtrum, wide mouth, dental abnormalities, puffy cheeks, micrognathia, low-set ears). When associated with idiopathic hypercalcemia of infancy, this form is known as Williams syndrome. Subvalvular AS caused by a congenital membrane or fibrous ring just beneath the aortic valve is uncommon.
Pathophysiology
Aortic regurgitation may accompany AS, and about 60% of patients > 60 yr with significant AS also have mitral annular calcification, which may lead to significant mitral regurgitation.
The increased pressure load imposed by AS results in compensatory hypertrophy of the left ventricle (LV) without cavity enlargement (concentric hypertrophy). As the pressure gradient across the aortic valve increases, , wall stress (afterload) increases, causing LV cavity enlargement, reduced ejection fraction (EF) and a misleadingly low gradient across the aortic valve (low gradient severe AS). Patients with other disorders that also cause LV enlargement and reduced EF (eg, MI, intrinsic cardiomyopathy) may generate insufficient flow to fully open a sclerotic valve and have an apparently smallvalve area even when their AS is not particularly severe (pseudosevere AS). Pseudosevere AS must be differentiated from low gradient severe AS because only patients with low gradient severe AS benefit from valve replacement.
Elevated shear stress across the stenosed aortic valve degrades von Willebrand factor multimers. The resulting coagulopathy may cause GI bleeding in patients with angiodysplasia (Heyde syndrome).
Symptoms and Signs
Congenital AS is usually asymptomatic until at least age 10 or 20 yr, when symptoms may begin to develop insidiously. In all forms, progressive untreated AS ultimately results in exertional syncope, angina, and dyspnea (SAD triad). Other symptoms and signs may include those of heart failure and arrhythmias, including ventricular fibrillation leading to sudden death.
Exertional syncope occurs because cardiac output cannot increase enough to meet the demands of physical activity. Nonexertional syncope may result from altered baroreceptor responses or ventricular tachycardia. Exertional angina pectoris affects about two thirds of patients; about half have significant coronary artery atherosclerosis, and half have normal coronary arteries but have ischemia induced by LV hypertrophy, altered coronary flow dynamics, or both.
There are no visible signs of AS. Palpable signs include carotid and peripheral pulses that are reduced in amplitude and slow rising (pulsus parvus, mollus et tardus) and an apical impulse that is sustained (thrusts with the 1st heart sound [S1] and relaxes with the 2nd heart sound [S2]) because of LV hypertrophy. The LV impulse may become displaced when systolic dysfunction develops. A palpable 4th heart sound (S4), felt best at the apex, and a systolic thrill, corresponding with the murmur of AS and felt best at the left upper sternal border, are occasionally present in severe cases. Systolic BP may be high with mild or moderate AS and falls as AS becomes more severe.
On auscultation, S1 is normal and S2 is single because aortic valve closing is delayed and merges with the pulmonic (P2) component of S2. The aortic component may also be soft. Paradoxical splitting of S2 may be heard. A normally split S2 is the only physical finding that reliably excludes severe AS. An S4 may be audible. An ejection click may also be audible early after S1 in patients with congenital bicuspid AS when valve leaflets are stiff but not completely immobile. The click does not change with dynamic maneuvers.
The hallmark finding is a crescendo-decrescendo ejection murmur, heard best with the diaphragm of the stethoscope at the right and left upper sternal border when a patient who is sitting upright leans forward. The murmur typically radiates to the right clavicle and both carotid arteries (left often louder than right) and has a harsh or grating quality. But in elderly patients, vibration of the unfused cusps of calcified aortic valve leaflets may transmit a louder, more high-pitched, “cooing” or musical sound to the cardiac apex, with softening or absence of the murmur parasternally (Gallavardin phenomenon), thereby mimicking mitral regurgitation. The murmur is soft when stenosis is less severe, grows louder as stenosis progresses, and becomes longer and peaks in volume later in systole (ie, crescendo phase becomes longer and decrescendo phase becomes shorter) as stenosis becomes more severe. As LV contractility decreases in critical AS, the murmur becomes softer and shorter. The intensity of the murmur may therefore be misleading in these circumstances.
The murmur of AS typically increases with maneuvers that increase LV volume and contractility (eg, leg-raising, squatting, Valsalva release, after a ventricular premature beat) and decreases with maneuvers that decrease LV volume (Valsalva maneuver) or increase afterload (isometric handgrip). These dynamic maneuvers have the opposite effect on the murmur of hypertrophic cardiomyopathy, which can otherwise resemble that of AS. The murmur of mitral regurgitation due to prolapse of the posterior leaflet may also mimic AS.
Diagnosis
Diagnosis is suspected clinically and confirmed by echocardiography. Two-dimensional transthoracic echocardiography is used to identify a stenotic aortic valve and possible causes, to quantify LV hypertrophy and degree of systolic dysfunction, and to detect coexisting valvular heart disorders (aortic regurgitation, mitral valve disorders) and complications (eg, endocarditis). Doppler echocardiography is used to quantify degree of stenosis by measuring jet velocity, transvalvular systolic pressure gradient, and aortic valve area.
Severe stenosis criteria are a peak aortic jet velocity > 4 m/s, mean gradient > 40 mm Hg, valve area < 1.0 cm2 The gradient may be overestimated in aortic regurgitation and underestimated in LV systolic dysfunction.
Cardiac catheterization is necessary to determine whether coronary artery disease (CAD) is the cause of angina and, occasionally, to resolve inconsistency between clinical and echocardiographic findings.
An ECG and chest x-ray are obtained. ECG typically shows changes of LV hypertrophy with or without an ischemic ST- and T-wave pattern. Chest x-ray findings may include calcification of the aortic cusps (seen on the lateral projection or on fluoroscopy) and evidence of HF. Heart size may be normal or only mildly enlarged.
In otherwise asymptomatic patients with severe AS, closely supervised exercise ECG testing is recommended because it may elicit symptoms of angina or dyspnea. If these symptoms are due to the severe AS, intervention is indicated. Failure to normally increase BP and development of ST segment depression are less predictive of adverse prognosis. Exercise testing is contraindicated in symptomatic patients.
Prognosis
AS progresses faster as severity increases, but the wide variability in progression rates requires regular surveillance, particularly in sedentary elderly patients. In such patients, flow may become significantly compromised without triggering symptoms.
Asymptomatic patients with severe AS and normal systolic function should be reevaluated every 6 mo because 3 to 6% will develop symptoms or LVEF depression every year. The risk of surgery outweighs the survival benefit in asymptomatic patients, but with the onset of symptoms the mean survival plummets to 2 to 3 years and prompt valve replacement is indicated to relieve symptoms and improve survival. Risk with surgery increases for patients who require simultaneous coronary artery bypass graft (CABG) and for those with depressed systolic LV function.
In patients with severe AS, about 50% of deaths occur suddenly and they should be advised to limit physical exertion.
Treatment
Asymptomatic patients with a maximum gradient ≤ 25 mm Hg and a valve area > 1.0 cm2 have a low mortality and low overall risk of requiring surgery in the next 2 yr; annual evaluation for symptom progression, including echocardiography to determine gradient and valve area, is appropriate.
Asymptomatic patients with gradients of 25 to 50 mm Hg or valve area < 1.0 cm2 are at higher risk of developing symptoms in the next 2 yr, but elective valve replacement is not usually required in the absence of symptoms. Valve replacement is indicated for patients who have moderate or severe AS and primarily require CABG. Nothing has yet been proved to slow the progression of AS; randomized trials of statin therapy have been negative.
Drugs that can cause hypotension (eg, nitrates) should be used cautiously, although nitroprusside has been used as a temporizing measure to reduce afterload in patients with decompensated heart failure in the hours before valve replacement. Patients who develop heart failure but are too high risk for valve intervention will benefit from cautious treatment with digoxin, diuretics, and ACE inhibitors.
Symptomatic patients (including those with symptoms only on exercise testing) should undergo valve replacement or balloon valvotomy. Few asymptomatic patients benefit from valve intervention, but possible exceptions include those with very severe AS (peak velocity > 5.5 m/sec) or those with rapidly progressive stenosis (> 0.3 m/sec per year). Valve replacement is indicated for virtually all patients who can tolerate surgery. In younger patients, the patient's own pulmonic valve can be used, providing good durability; a bioprosthesis is then used to replace the pulmonic valve (Ross procedure). Most often, the aortic valve is replaced with a mechanical or bioprosthetic valve. Preoperative evaluation for CAD is indicated so that CABG and valve replacement, if indicated, can be done during the same procedure.
Balloon valvotomy is used primarily in children and very young adults with congenital AS. In older patients who are not candidates for surgery, balloon valvuloplasty is less often used because it has a high complication rate and provides only temporary relief of symptoms. Instead, percutaneous transcatheter valve replacement (TAVI) is being developed and appears better than medical therapy and about equivalent to surgical replacement, although increased rates of stroke occur up to 1 yr postprocedure.
Key Points
Last full review/revision November 2012 by Guy P. Armstrong
Content last modified December 2012
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